The present invention relates to wood burning stoves of the airtight variety, although in one operational mode of the invention, the stove can be used to burn coal.
In recent years, due primarily to the energy crisis, wood burning stoves have enjoyed an ever-increasing popularity and public acceptance. The ultimate objective in stoves of this type is to achieve as complete combustion as possible of the combustion gases, since with more efficient combustion, burn time can be increased because it is possible to slow the fire down and still obtain the desired heat transfer for maximum comfort. However, most existing stoves of this type, i.e. airtight wood burning stoves, have a combustion efficiency somewhere in the range of fifty to sixty percent, primarily due to the fact that the ignition point of combustion gases is in the general range of 1300.degree. F. whereas the temperatures generated in stoves of this type are usually in the range of 500.degree. and 900.degree. F. Thus, efficient combustion of these combustion gases has been difficult, if not impossible, to achieve, resulting in lower combustion efficiency, which in turn results in creosote build-up in the chimney or flue, which build-up frequently results in chimney fires. Also, reduced combustion efficiency results in undesirable smoke pollution.
In co-pending U.S. application Ser. No. 136,687, filed Apr. 2, 1980 by Peter S. Albertsen, one of the co-inventors of this application, the concept of using a catalytic converter in stoves of this type of obtain greatly increased combustion efficiency is disclosed. Specifically, by causing the combustion gases to flow through a catalytic converter before reaching the exhaust duct or flue of the stove, the ignition point of the escaping combustion gases is lowered to the general range of 500.degree. F., thus resulting in almost complete afterburn of these gases in the normal range of operating temperatures in stoves of this type. This results in combustion efficiency in the general range of ninety percent, or in other words, an efficiency of approximately thirty-five percent more than that achieved by traditional airtight woodburning stoves. This increased efficiency means little or no pollution will enter the atmosphere because the smoke, a normal by-product of conventional wood stoves, is virtually eliminated, leaving a harmless humid vapor in its place. In addition, as a result of the almost perfect combustion that takes place, there is virtually no creosote build-up in the chimney, thus greatly reducing chimney fire hazards and at the same time reducing chimney maintenance. Furthermore, peak performance can be obtained even with the use of soft and unseasoned wood and burn time can be increased because it is possible to slow the fire down and still maintain almost perfect combustion while transferring heat temperatures necessary for maximum comfort.
The present invention is also directed to the use of catalytic converters in wood stoves, and is particularly directed to an improved baffle system used in connection therewith. More specifically, as suggested in the aforesaid co-pending Albertsen application, it is desired to have all of the combustion gases pass through the catalytic converter when the stove is in its normal operating mode. However, since the catalytic converter is in the nature of a filter which to some degree resists or impedes the flow of combustion gases therethrough, it will be apparent that when the access door of the stove is opened, the combustion gases and smoke would follow the path of least resistance and would billow outwardly through the open access door. In order to prevent this, the co-pending Albertsen application discloses damper means which, when the access door of the stove is opened, automatically move by gravity to a position permitting direct access to the exhaust duct or flue of the stove, so that the combustion gases and smoke will be exhausted through the flue, rather than spilling into the room through the open access door.
The present invention achieves these same basic objectives by an improved damper system. Specifically, the damper of the present invention is manually controlled, rather than gravity controlled, thus eliminating the possibility of the damper inadvertently jamming or sticking in closed position when the access door of the stove is opened. In order to insure that the damper moves to its proper position when the access door of the stove is opened, handle means for manually manipulating the damper from outside the stove are provided, said handle means physically preventing the access door of the stove from opening until said handle means is moved to a predetermined position, said predetermined position regulating the damper so that flow of the combustion gases through the converter is blocked, and direct flow of the combustion gases to the stove exhaust is opened. Thus, in the present invention, the access door of the stove cannot be opened until the damper has positively been moved to its proper position.
In addition, with the stove in its normal operating mode, i.e. with the door of the stove closed and with combustion gases passing through the catalytic converter, the possibility exists that the catalytic converter may on occasion become blocked or clogged, primarily due to the burning of improper materials in the stove. Should this happen, there would be no place for the combustion gases and smoke to go, and hence said gases and smoke would force themselves out through the front opening of the stove, notwithstanding the fact that the access door is in closed position. This, of course, would result in undesirable smoke spillage into the room in which the stove is located. In order to prevent this, the damper of the present invention has been specifically designed with a controlled leakage factor, i.e. controlled leakage through the damper to the exhaust duct is possible, even when the damper is closing off the access opening to said duct. As a result of this built-in controlled leakage, should the catalytic converter become blocked or clogged, combustion gases and smoke still can pass through the closed damper to the exhaust duct, rather than spilling into the room around the door of the stove. This is an important feature of the present invention.
In addition, the damper system of the present invention permits the stove to assume an operational mode where coal can be burned instead of wood. This is not possible in the aforesaid co-pending Albertsen application.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.